Apparatus and method for logging boreholes with formation testing fluids



Oct. 5, 1965- SUBSTITUTE FOR MISSING )4R Or'iginal Filed April 24, 1958M. C TERRY APPARATUS AND METHOD FOR LOGGING BOREHOLES WITH FORMATIONTESTING FLUIDS 2 Sheets-f3heet l Oct. 5, 1965. M, C, TERRY 3,209,588 vAPPARATUS AND METHOD FOR LOGGING BOREHOLES WITH FORMATION TESTING FLUIDSOriginal Filed April 24, 1958 A2 Sheets-Sheet 2 PRESSURTZED. l MOTORPREss'uRlzEo 4 WATER CHAMBER 9 on. CHAMBER RUBBER SHOE TLRESISTIVITY-ELECTRODE' NDUCTVITY CELL Mun HAMaER |40 ooL BELLows` .35cHlJArER 57 yFIGZ.

` INVENTOR.

ATTORNEYv l 3,209,588 APPARATUS AND METHOD FOR LOGGING BORE- IIOLES WITH'FORMAT ION TESTING FLUIDS Melvin C. Terry, Houston, Tex., assignor, bymesne assignments, to Esso Production Research Company, Houston, Tex., acorporation of- Delaware Continuation of application Ser. No. 730,638,Apr. 24, 1958. This application Mar. 3, 1961, Ser. No. 94,115

13 Claims. (Cl. 73--152) This is a continuation of application SerialNo. 730,638 of Melvin C. Terry for Well Logging Method and Apparatusfiled April 24, 1958. y

This invention relates to the vdetermination of characteristics of earthformations, and more particularly to techniques for determiningcharacteristics of earth formations that involve the injection ofdia'gnosticlfluids behind a filter cake lining the wallof a borehole inthe earth.

To determinethe characteristics of earth formations around a borehole,it is often desirable to inject a diagnostic fluid through the filtercake that lines the wall of the borehole. For example, in connectionwith well logging operations it may be desirable to inject an oxi-vdizing agent such as perchloric acid behind-,the filter cake.- Changesin temperature in the earth formations contacted by the acid may beindicativeof the presence of hydrocarbons in the formations'. As anotherexample, surface-active reverse wetting agents consisting of a'cationicsalt may be injected behind a filter cake in connee-,

tion with resistivity logning of boreholes in the manner described inUS. Patent No. 2,873,423--J- W. Graham et all In order to inject testingfluids into earth formations, it

maybe necessary or desirable to remove the filter cake` .lining theborehole.

However, when the borehole mud pressure is higher than the pressure ofconnate fluids in the formation, it has been found extremely ditlicult,if not impossible, to scrape away the filter cake and to inject fluidinto the exposed earth formation. Thereason for this difficulty appearsto be that the filter -cake is re-formed assoon as it is scraped away ifthe borehole mud pressure is greater than earth formation fluidpressure.

In accordance with the teachings of4 this invention, a portion ot afilter cake surface is isolated from borehole pressure, for example, bymeans of a suitable caisson or other rigid-walled isolating-means. Thepressure on the portion of the filter cake surface thus isolatedis.reduced below the pressure exerted on` the Afilter `cake by connateearth formation fluids. Formation fluids will tend to flow out oftheformation; and if the pressure is sufficiently reduced, the filter cakemay rupture and wash away. Testing fluids may then be injected into theea-rth formation through the perforation in the filter cake resultingfrom the washing away of the ruptured cake. l

According to a more specific aspect of the invention, to aid formationfluids in washing away the filter cake, the selected, portion of thesurface of the filter cake may be subjected to fluid flow from aflexible reservoir subject to borehole pressure. The washing'` fluidwithin thc fluid reservoir may include testing chemicals such as reversewetting surfactants consisting of a cationic salt. Such reverse wettingagents alter the capillary action of earth formations to cause them tobecome preferentially oil wet. The significance of resistivity tests onthe earth formation is substantially enhanced` by treatment with suchsurface-active reverse wetting agents.

Various objects and features of the invention, including those which maybe gathered from 'theabove discus- D United States Patent t) CIIPatented ct. 5, 1965 rice sion, will become apparent from the followingdescription considered in connection with the accompanying drawings,wherein:

.FlG. 1 is a simplified schematic presentation of an -embodiment of theapparatus of the invention;

FIG. 2 is a more detailed presentation, partially incross l section, ofthe apparatus shown in FIG.,1;

FIG. 3 is a -front view of a portion of-the of FIG. 2;

FIG. 4 is a sectional sideview of the apparatus of FIG.4 3j and FIG. 5is a View similar to FIG. 4 illustrating a modification of theinvention. l

'The invention will first be described with reference-to theembodimentillustrated in FIGS. 1, 2, 3, and 4. FIG. l an instrumenthousing 7 is shown suspended from logging cable 5 within vborehole 1.l

the borehole during drilling operations. instrument housing 7 is open toborehole pressure (i.e., the pressure exerted yby the drilling fluid inthey vicinity of-the housing) through openings 21. The instrumenthousing may be an elongated cylinder constructed according to knowntechniques for logging srndes.

The instrument housing carries a deformable pad or shoe 31 of rubber orrubber-like material having a central opening 33. The pad surrounds theopen end of" :t caisson or rigid-walled container v10i). When the `padis rammed against the surfnet` ol filter cake v3, it is adapted toisolate a section dcncd by the opening 33. The function of p nd 3l is toprovide a fluid seal between the edge of the opening33 and filter cakev3 so as to prevent entry of borehole fluids into the caisson. The rubbershoe is hydraulically rammed against the filter cake b'y apparatusincluding back-up plate 29; this ramming apparatus will be described inmore detail below. The r` bbe'r pad 31, back-up plate 29. and certain ofthe associated apparatus may be substantially the same as the apparatusdescribed. by M. Lebourg et al. in Paper No. 701G presented at the fall1956 meeting of the American Institute of .Mining and MetallurgicalEngineers in Los Angeles, California.

Caisson 100 encloscs a container 104 which is affixed to and suitablyspaced from caisson 100 soas to leave a space or passageway 109 betweenthe caisson 100 and container 104. lContainer 104vv houses a porousmedium 103 which may substantially fill the interior of the container.Container 104 is open-ended, and porous medium 103 protrudes through thepassageway. y The porous medium ,may consist of a block of carborundum,sandstone, sintered glass, silica, or a permeable, porous ceramic. Thefunction of porous medium 103 is to disperse liquids injccted into thesystem so that the liquids will contact as large an area as possible ofthe filter cake or earth formation against which the porous medium ispressed.

As shown most perspicuously in FIGS. l and 2, a pair' of flexible fluidreservoirs 25 and 27 are provided within which are stored water (inreservoir 25) and acid (in reservoir 27). Reservoir 27 is housed withinreservoir 25, and reservoir 25 is exposed to borehole pressure by way ofbellows 23.' Acid reservoir 27 is hydraulically coupled to the interiorof container |04 through a constriction 93,

While tube 102 may terminate at the rear of porous medium 103, in FIG. 4it is shown as extending through the apparatus The borehole` is linedwith a filter' cake 3 deposited on the Walls of" The interior of` anddeformable pad 31 away from the wal-l of the boreporous medium 103 sothat fluids from tube 10.?. will be spraged directly against the filtercake or earth formation,

Yfhe acid to be stored in acid bag 27 may be perchloric acid or oneofthe other suitable ovidizing agents described in Patent No.2,708,155-5. E. Buckley et al. The bag or reservoir within which theacid is stored should be resistant to the particular acid used. Whenperchlorie acid is used, it nas been found that Kel-F rubber is asuitable material for the acid bag.

The watcrin reservoir may include a sllitable reverse wetting surfactantsuch as described in the nforecited U.S. Patent No. 2,873,423.

A vertical groove 110 may be cut in the face of porous medium 103 forthe purpose of protecting a platinum wire 111 or `other suitabledcvicefor measuring temperature it should be noted that unless theconnectors are suitably insulated from the caisson, the caisson shouldbe made of an electrically insulative material. The Connectors 106 and108 may bc connected lo a suitable telemetering arrangement fortransmitting thev changes in resistivity of wire- 111 up the borehole oncable 5 to the carths surface.

lt should be noted that the acid bag 27 and water reservoir 25 .shouldbe positioned above caisson 100 so that fluid will readily flowtherefrom.

Dei'ormable shoe or pad 3l is rammed against thefilter cake by apparatusincluding back-up plate 29, pistons 107, 11), 129. and 135 withinchambers 113, 121. 131, and 137. respectively, and tension springs 117.,114-, 12,5. and "the tension springs normally pull back-up plate 29hole. When pressurized fluidis injected into chambers 113,121, 131, and137, thc forces on the pistons will force back-up plate 29 and pad 3linto tirm enga-gement with the filter calle lining the borehole. Asuitable hydraulic pressure for this purpose is about 450() pounds persquare inch.

. duit system'V 69 and the interior of chamber 15 is cut ofl'. Conduitsystem 69 also opens into a chamber 71v cane 3, it will be virtuallyimpossible to dislodge in-.

strument housing 7. Therefore, there is provided a, failsafe systemincluding valve 63 (which couples conduit system 51 to conduit system 69when electromagnetieally actuated valve 63. is opened) andelectromagnetically actuated valve 65, which when unactuated cou-plesconduit: system 69- to the interior of chamber 15. Upon actuation ofvalve 65, fluid communication between conwithin val-ve y70. Valve stem'79 is moved downwardly against the pressure of coil spring 73 bydifferential pressure across piston 75. When valve stem 79 is in its4lowermost lposition as shown, the lower end of the stem cuts off fluidcommunication between ports 80 and-77. Port 80 is coupled to port 64 ofpressure'reversing and amplii Thus, should there be a ton'75. Valve stem79 will move upwardly, relieving Vl:

the differential pressure across piston 41and cmoving the pressure onpistons 107, 119, 129, and 135 so t'lat tension springs 112, 114, 125,and 138 can retract bat-loup The pressure for actuating thepistons 107,119, 129, i

and 135 sderived from an electric motor-driven suction pump 13 and apressure amplifying and reversing apparatus 38. Pressure gauge 53measures the pressure .across pump 13. The inlet of suction pump 13 isconnected to several oil filled hydraulic circuits,l and the outlet ofthe pump discharges into a ch nnber 15. Chamber 15 is hy' draulicallycoupled to a bellows 19 exposed to borehole Thus. suction pump 13discharges into a fluid mediumexposed to borehole pressure,

Pressure amplifying and reversing means 38 includes a piston cylinder39, the open end of'which works against the oil in chamber 15 (and thusagainst borehole pres- 'i piston cylinders 113, 121,v 131,. and 137. Thedifferential pressure across piston 41 will tend to move pistons 41 and45 downwardly. The differential pressure will be amplified because ofthc difference in the areas of the` faces of pistons 41 and 45. Inasmuchas piston 45 works against a virtually incompressible liquid, the liquidwill exert pressure on pistons 107, 119, 129, and 135 to force thepistonsoutwardly from 'housing 7. Thus, with valve 61 open, the ultimateeffect of suction pump 13 will be to force pistons 107 and 135 to moveto the left as ShOWH,

plate 29 and pad 3l. l y

For the purpose of lowering the pressure in opening or.space 109, thereis provi/.lcd a rigid-walled mud Achun- `ber 37 hydraulically coupled tothe space 109 by conduit l 139, and an oil filled bellows 35 withinchamber 37. coupled to the inlet 54 of suction pump 13 by fluid conduit85,- normally closed electromagnetically actuated valve 59, and conduitsystem 51. Bellows- 35 and conduit 85 are at all times lled with oil.When valve 59 is open, suction pump 13 will draw oil out of bellows 35to reduce the`pressure within chamber 37. Thus, the pressure in Space109 and on the surface of the portion of the filter cake defined bycaisson 100 and deformable pad 31 will. be substantially lowered. Avalve arrangement 83 sim-y striction 93 is readily determinable, so thevolume of fluid passing through constriction 93 to porous medi-um 103canbe easily calculated.

The function of pressure gauge 91 is to produce an output signalindicative of the pressure being measured by the gauge. The electricalsignals may be transmitted to the earths surface by a suitabletransmission system.

Separate electrical leads fromthe earths surface may'y control each ofthe electromagnetieally actuatedfvalv'es described above, or a suitableremote control system,

may be utilized for controlling the actuation of the valves with aminimum number of wires in the cable from which `the instrument housingis suspended.

The operation of the apparatus described yabove `is as follows. Let itbe assumed that instrumenthousing 7 lhas been lowered into a boreholeuntil rubber pad 31 is adjacent an earth formation on. which it isdesired to run a test. Electric motor 9.is energized-to drive suctionpump 13, and valves 63 and 65 are actuated to close valve 65 and openvalve 63. The differential pressure applied across piston will closeport 80. Valve 63 now may be closed. Valve 61 now may be opened; sinceport is no longer *open to tiuid communication with port 83 are moveddownwardly so that conduit 85 is no longer open' to the pressure withinchamber 15 through the ports of valve 83. When valve 59 is opened,bellows 35 will contract to decrease the pressure within space 109 so.that earth fluids will flow against the filter cake 3. When valve 97 isopened, water will be directed against filterl cake 3 to aid the flu-idsfrom earth formation 28 to wash away the filter cake. Particles of thefilter cake, the wash water from reservoir 25, and earth formationfluids will flow through space 109, conduit 139', and will be stored inmud chamber 37. Conductivity measuring cell 140 in conduit 139 isinserted to measure the conductivity of fluids flowing through conduit139.v Cell 140'may consist of a pair of insulated electrodes coupled to`a potential source through suitable current measuring apparatus. Theelectrical signals produced by conductivity cell 140 are transmitted to'the earths surface to provide the operators with an indication ofthenature of the fluids passing through conduit 139. l

As soon as the output signals from conductivity cell lift) indicate thatformation fluids a-re flowingfreelyinto mud .Y

may be opened, a predetermined amount of perehloric acid may be allowedto flow through conduit 99 and porous medium 103 tocontact earth.formation 28, and the change in temperature indicated by the change inresistivity'of platinum wire 111 may be noted. Pad 31 and backup plate29 may now be retracted either by (le-energizing the actuating coil ofvalve 65 or by energizing the actuating coils of valves 61 and 57. Thiswill remove the pressure on pistons 107, 119, 129, and to retract thepad and back-up plate. The instrument housing now either may be broughtto the earths surface or may berepositioned in the borehole for anothermeasurement.

It is possible to estimate certain of the properties of the earthformations from pressure gauge readings of the pressure in caisson 100.For example, the pressure maintained during the pumping operation afterthe filter cake is broken will depend on the pumping rate (which will bemore or less constant) and formation permeability. When `the pump isstopped, the pressure will come to that of the formation. Formationpermeability will be indicated by the equilibrium pressure attained, therate at which the pressure in thc caisson'rises to formation pressure,and the rate at which the various fluids may be injected.

lflG. 5 illustrates another embodiment of the invention which is adaptedfor use when the filter cake is unusually thick. When the filter cake isunusually thick,`it maybe difficult for porous medium'103 to contactearth formations after a portion of the filter' cake adjacent the mediumhas been removed. Inner container '104 for porous mcdi'um 103 issupported by guides 165 and is adapted to move to the right and left asviewed in FIG. 5. The con'- tainer is norm-ally biased to the left bycoil springs 159 6 piston 157 through port 166. Water line 101 and aridline 99 are connected together near end plate 153 and are iniected intacontainer 104 through nipple 151 and the interior of container neck 161`Acid valve 95 and water valve 97 should be as close as possible to thejuncture of lines 99 and 101 and to 4end plate 153.

The operation of the apparatus of FIG. 5 differs from that of theembodiment of FIGS. l through 4 in that fluid t pressure applied tochamber will force container 104 and medium 103 to the right asthefilter cake disintegrates. In due course, guides 165 will strike stopmembers 163, and springs 159 will be completely compressed. Note alsothat wash water will filter through the porous medium 103 tot-'aidformation fluids in washing away the filter cake.

Various changes maybe made in the above-described invention, anddifferent embodimentsof the invention may be made without departing fromthe spirit and scope thereof. Therefore, it is intended that all of thematter coutained'in the above description and shown in the accompanyingdrawings shall be construed as illustrative and not in a limiting sense.l

What is claimed is: 1. Apparatus for removing a portion of a filter cakelining the wallof a borehole and linjecting formation,

of said borehole when said open end abuis said filter cake; means forabutting said opcnend against u portion Of said filter culte; meanshydraulically coupled to the interior of said container for reducing thepressure within said container to a pressure less than the pressureexerted by earth formation fluid on said portion of said filter cake toperforate said portion of said filter cake; and means for injecting saidtesting fluids through said lining for said block so that said testingfluids can filter through said block and through the perforationproduced by perforating the filter cake into the earth formations.

2. Apparatus for removing a portion of a filter cake r lining the wallof a borehole and injecting formation testing fluids into earthformations behind said filter cake,

comprising: a fluid permeable block; a first fluid impermeable'container for said block; a second `fluid impermeable container for saidfirst container, spaced from said first container; said first and secondcontainers each having an open side to permit said block to contact saidfilter cake; means for effecting va fluid-tight seal between said filtercake and said second container aroundrsaid open side of said secondcontainer; means forlowering the pressure in the space between saidfirst and second containers to draw earth formation fluids. through saidfilter cake in sufficient volume to wash away at least a` portion of thefilter cake through which said formation fluids pass; and meansconnected to said first container for controllably injecting saidformation testing .fluids through said fluid permeable block.

3. Apparatus for injecting formation testing fluids into .earthformationsbehiml a filter cake lining the. wall of .a borehole,comprising: a rigid-walled caisson, said caisson having an open endadapted to be positioned y against said filter cake; means connected tosaid `caissonfor` effecting a fluid-tight seal between said caisson andsaid filter' cake to prevent entryinto said caisson of fluids withinsaid borehole; means connected to said caisson for lowering the'pressurewithin said caisson relative to borehole pressure to produce adifferential pressure across said filter cake to effect a flow offormation fluids into said caisson of sufficient magnitude to wash awayat which bear against piston 157. Fluid pressure from conduit 49 isapplied to the space between end plate 153 and le'ast a portion of thefiltercake through which said earth formation fluids flow; and meansconnected to said caisson for controllably injecting said testing fluidsthrough said caisson into said earth formations.

4. Apparatus for testing earth formations traversed by tainer; firstelectrically actuated v alvc means; a bellows within said chamber, andfluid conduit means coupling' the interior of said bellows to said pumpinlet through said first electrically-actuated valve means uponactuation of i-.aid valve means; coupling means including secondelectrically actuated valve means'hydraulically'coupling the interior ofsaid first fluid reservoir to the interior of said second'container;coupling means including third electrically actuated valve meanshydraulically coupling the interior of said vsecond fluid reservoir tosaid second container; a deformable pad affixed to said first containeraround said open end thereof adapted to provide a fluidtight sealagainst entry of fluids from said borehole inifi said first and secondcontainers; a hydraulically ac tuublc ram foriforcing said pad, saidfirst container, and said porous block against said filter cake; andpressure reversing means and fourth electrically actuable valve meanscoupling said pump inlet v to said i'am for application of n positivepressure to said ram i'e'lative to borehole presf is actuated; saidfirst, second, third, and fourth valve iii to actuate said ram when saidfourth valve means means being vindividually actuable by electricalconnccthrough said open end of said first container; first and secondflexible fluid reservoirs exposed to borehole pressure; a suction pumphaving an inlet and outlet, adapted to work against borehole pressure atits outlet; a rigidwalled chamber; fluid conduit' means hydraulicallycoupling said rigidwalled chamber with the interior of said ll ll firstcontainer; first electrically actuated valve means; a bellows withinsaid chamber, and fluid conduit means coupling the interior of-saidbellows to said pump inlet through said first electrically actuatedvalve means upon actuation of said valve means; coupling means includingsecond electrically actuated valve mea-ns hydraulically coupling theinterior ofsaid first fluid reservoir tothe interior of said secondcontainer; coupling means including third electrically actuated valvevmeans hydraulically coupling the interior of saidsecond fluid reservoirto said second container; a deformable pad affixed 'to said firstcontainer around said open en'd thereof adapted to provide afluid-tightseal against'entry offluids withinl said borehole intosaidfirst and second containers; a' hydraulically actuable ram for forcingsaid pad, said first container, and said vporous block against saidfiltcr cake; and pressure 'reversing means and fourth valve electricallyactuable means coupling said-pump inlet to said ram for application of apositive pressure to said ram relative to borehole pressure to'actuatesaid ram when said fourth valve means 4is actuated; said first, second,third, and fourth valve means being individually actuable by electricalconnections to the earths surface.:

6, Apparatus for testing carth formations travei-,ed

by a borehole, comprising: a first container having an open end; aporous block', a second open-ended container within said/firstcontainer, said second container being adapted to at least partiallyenclose said porous biocl; so

that an exposed face of said porous block protrudes coupling theinterior of said bellows to said pump inlet through first electricallyactuated valve means upon actuation of said valve means; coupling meansincluding second ,electrically actuated valve means hydraulicallycoupling th'evintcrior of said lfirst fluid reservoir to the interior ofsaid second container; coupling means inclu ling third electricallyactuated valve means hydraulically coupling the interior of said secondfluid reservoir to said second container; a deformable pad affixed tosaid first container around said open end thereof adanted to Aprovide afliiidtight seal against entry of fluids .xithln -said borehole intosaid first and second containers: a

hydraulically actiiahle i'ani for forcing said pad. aid first containerand said porous block againstsad filter cake; hydraulic nie-ans forforcing said secon-d container through said open end of said firstcontainer so that saidpoious blockis at all times in contact with saidfilter cake; and pressure reversing means and fourth cicctricallyactuablc valve means coupling said pump inlet to said ram forapplication of a positive pressure to said ram relative to boreholepressure to actuate said rain when said fourth valve means is actuated;said first, second, third, and fourth valve means being individuallyactuable 'by electrical connections to the earths surface.

7. Apparatus for perforating the filter cake lining the wall of aborehole, comprising: a rigid-walled caisson adapted to isolate 'aportion of the surface of said filter cake; deformable scaling inca'nsaffixed to said caisson for providing a fluid-tight seal between theedge of said caisson and the filter cake against which said edge abuts;means hydraulically connected to the interior of said caisson forreducing the pressure within said Caisson below thcwpressure of theformation fluid in the earth formation adjacent said portion of saidfilter ca'kc stirface to produce flow of formation fluids throughsaidfilter cake into said caisson sufficient to wash away asection of saidfilter cake; and means for simultaneously injecting washing fluidthrough said caisson `against said por-tion of said filter cake surface.

8. Apparatus for injecting fluids into earth formations through aborehole filter cake while said borehole is subject to a pressure ofpredcterminable magnitude, comprising: an elongated housing 4memberhousing afirstf vflexible reservoir for said fluids, a secondl'reservoir for receiving earth' formation fluid, a third flexiblereservoir enclosing said first flexible reservoir and a predeterminedquantity of water, a deformable pad surrounding a metallic caisson meansadapted to abut against a portion of the surface of said filter cake toisolate said portion. and the Space enclosed by said caisson means fromsaid horc-4 liole, and hydraulically actuated means for riunniing .saidpad against the wall of said borehole to provide afluidtight seal forsaid portion of said filter cake surface; suction pump means adapted toproduce a pressure less than borehole pressure in the vicinity of saidhousing member; means, including first normally closed electricallyaetuable valve means and said second reservoir, c-oupled to said pumpmeans and to the interior of said i Y mation fluid through said filtercake; means including second normally closed electrically actuable valvemeans, hydraulically coupling said first reservoir to the interior ofsaid lcaisson adapted to inject fluid within said.first reservoir intovsaid caisson means; means including third electrically actuable,normally closed valve means, hydraulically coupling said third reservoirto the interior of said caisson adapted to inject fluidwithin said thirdreservoir into said caisson; andmeans -including fourth normally closedelectrically actuable valve meansl and pressure reversing andvamplifyingmeans coupling said pump to said hydraulically actuable means adapted,upon actuation of said valve means, lto apply a pressure to saidhydraulically actuable means that isv greater than borehole pressure toactuate said hydraulically actttable means; all of said valve meansbeing selectively actuable from a remote-location.

9. Apparatus for determining the nature ofV fluids in earth formationssurrounding a borehole having alfilter cakel on the wall thereof,comprising: a first housing means adapted to be lowered into saidborehole; an

annular, deformable pad having a central opening affixed to said firsthousing means;'hydraulically ,actuated jacking means carried by saidfirst housing means, adapted when actuated to ram said pad against saidfilter'cake to form a fluid-tight seal between said pad and said filtercake; caisson means aixed to said pad adapted to isolate the portion ofsaid filter cake defined by said pad from said borehole; tension springmeans affixedI to said housing and to said pad and said jacking meansadapted to normally constrain said jacking means and saidpad away fromthe sides of said borehole; a porous solid within 4said second housingmeans positioned to abutagainst said portion of said filter4 cake andsupported by a fluidtight container affixed to said caisson; saidcaisson'means and said container defining a generally annular spaceopening against said portion of said filter cake, through which fluidsfrom said porous solid and formation fluids may flow; a first fluidreservoir carried by said first housing and subject to boreholepressure;a second fluid reservoir within said first fluid reservoir; meansincluding electrically actuated valve means coupling said second fluidreservoir to said container toA permit the flow of said pad relative toborehole pressure around said pad;-

means, including pressure reversing and amplifying means and fourthelectrically actuated valve means, ,coupling said pump means to saidjacking means for actuating said jacking means by subjectingsaid jackingmeans to pressure greater than borehole pressure upon actuation of saidfourth valve means; sa-id hydraulic coupling means further including afluid-tight container hydraulically coupled to said generally annularspace and a fluid-filled bellows fiuidly coupled to said suction pumpmeans upon actuation Aof said third valve means; means for measuring theelectrical conductivity of liquids entering said generally annularspace; and means for electrically measuring physical changes produced byfluids from said second fluid reservoir when said fiuids contact earthformations adjacent said portion of said filter cake.

`10. Apparatus for injecting formation testing 'fluids into earthformations behind a. filter cake lining the wall of a borehole,comprising: a 4housingad'apted'to be passed through the borehole andpositioned opposite an earth formation under investigation; isolatingmeans carried by said housing and including a rigid hollow portionopening toward and having edges adapted to engage an earth forh mationunder investigation; means. for selectively urgingI said edges of saidhollow portion of said isolating means into scali-ng engagement withsaid borehole wall so .as to isolate the portion of said borehole w-allincluded within said edges; means connected to said isolating means forlselectively `lowering the pressure within said hollowy portion relativeto borehole pressureto produce a differential prcssu're across saidfilter cake to effect a flow of formudcake has formed, comprising thesteps of: isolating an area of the borehole wall including .any mudcakead; jacent thereto, selectively producing a pressure on the isolatedarea of the borehole wall that is less than the pressure of fluids inthe earth formations adjacent said area tto cause the fluids present inthe earth formations'ad jacent the isolated area to flush the mudcalclaway from said isolated area of the borehole wall and into an -are'aremoved from said isolated area, introducingafter-rc moval of saidmudcake an agent capable of -afl-:ctinga characteristic oltlie materialsin the earth 'fornuitions into a space contiguous with exposed portinsof said earth formations in the isolated area ot the borehole wall at apressure atleast equal to the pressure of the fluid Ipresent in theearth formations, and detecting uid char` acteristic of said materialsafter exposure to said agent.

12. A method for detecting the presence of oxidizable materials in earthformations traversed by. a lborehole on thc-sides of which mudcake lasformed. comprising the steps of:

isolating an area of the borehole wall including any mudfcake adjacentthereto; i

selectively establishing in a space continguous with said isolated areaa pressure substantially less than the pressure -ofuids present in theearth formations 4adjacent the isolated area so as to cause said fluidsto flush the mudcake out of and away from said isolated area of the:borehole wall and into an area removed from said isolatcd'arca;

subsequently 'introducing atte-r removal of` the mud cake an oxidizingagent capable of rcacting'with oxidizab'le materials in the earthformations into said space at a pressure at least equal to the pressureof the fluid present in the earth formations so as to causey adetectable reac-ton between -said oxidizing agent and any oxidizablematerials present in said formation; and detecting an increase intemperature lof a point within the area of influence of said detectablereaction representative of the occurrence of such a reaction.

13. A method for detecting the presence of oxidizable materials in`earthformations traversed yby a borehole on the sidesl of iwhichmudcakev has formed, comprising-the steps of;

isolating an area `of the borehole wall including any 'A mudcakeadjacent thereto; j selectively creating a pressure within a spacecontiguous `with said isolated arca of a magnitude sutil#l ciently'le-ss than the pressure of fluids present in the earth formationsadjacent the isolated area to cause said fluids to flush out and awayAthe mudcake fromy a pe-riod of time sufficient to remove enough mu dv A1 1' cake from aid isolated area to expose at least some portions ofsaid adjacent earth formations to contact with substances introducedinto said space;

subsequently introducing after removal of the mudcakc a predeterminedquantity of an oxidizing agent capable of reacting with ox'idizablematerials in the earth formations into said space contiguous with theexposed portions of said earth formations in the isolated area of theborehole wall at a pressure at `least 10 equalto the pressure of thefluids present in the earth .112 the influence of said reaction :':ndresulting there from', and providing an indication of said temperatureincrease representative of the presence of ox-idizable materials in theparticular earth formations under investigation.

References Cited by the Examiner UNTTED STATES PATENTS 2,338,372 l/44Wright 166-44' 2,696,262 411a/54 Power.; 166413 X` 2,983,586 5/61Blanchard 23-230 RiICHARDIC. QUEISSER, Primary Examiner. ROBERT L.EVANS` JOSEPH P. STRIZ AK, Examiners.

11. A METHOD FOR THE EXPLORATION OF MATERIALS IN EARTH FORMATIONSTRAVERSED BY A BOREHOLE ON THE SIDES OF WHICH MUDCAKE HAS FORMED,COMPRISING THE STEPS OF: ISOLATING AN AREA OF THE BOREHOLE WALLINCLUDING ANY MUDCAKE ADJACENT THERETO, SELECTIVELY PRODUCING A PRESSUREON THE ISOLATED AREA OF THE BOREHOLE WALL THAT IS LESS THAN THE PRESSUREOF FLUIDS IN THE EARTH FORMATIONS ADJACENT SAID AREA TO CAUSE THE FLUIDSPRESENT IN THE EARTH FORMATIONS ADJACENT THE ISOLATED AREA OF THEBOREHOLE WALL AND INTO AN AREA SAID ISOLATED AREA OF THE BOREHOLE WALLAND INTO AN AREA REMOVED FROM SAID ISOLATED AREA, INTRODUCING AFTERREMOVAL OF SAID MUDCAKE AN AGENT CAPABLE OF AFFECTING A CHARACTERISTICOF THE MATERIALS IN THE EARTH FORMATIONS INTO A SPACE CONTIGUOUS WITHEXPOSED PORTIONS OF SAID EARTH FORMATIONS IN THE ISOLATED AREA OF THEBOREHOLE WALL AT A PRESSURE AT LEAST EQUAL TO THE PRESSURE OF THE FLUIDPRESENT IN THE EARTH FORMATIONS, AND DETECTING AND CHARACTERISTIC OFSAID MATERIALS AFTER EXPOSURE TO SAID AGENT.